A 2 x 2 factorial design was employed in a quasi-experiment to investigate the effects of guidelines in group or individual settings on the calibration accuracy and achievement of 82 high school biology students. Significant main effects indicated that calibration practice with guidelines and practice in group settings increased prediction and postdiction accuracy. A significant interaction showed that students who practiced calibration in groups using guidelines showed the greatest accuracy in their predictions and postdictions. Students in the guidelines condition and in the group setting condition had significantly higher achievement scores. The findings of this study suggest that the use of guidelines and group settings can promote calibration accuracy and achievement in high school biology courses. (Contains 7 tables and 1 figure.)